Contribution of ATM and ATR kinase pathways to p53-mediated response in etoposide and methyl methanesulfonate induced DNA damage

Plant protein-derived anti-breast cancer peptides: sources, therapeutic approaches, mechanisms, and nanoparticle design

Breast cancer causes the deaths of approximately 685,000 women annually, posing a severe threat to women's health. Consequently, there is an urgent need for low-cost, low-toxicity and effective therapeutic methods to prevent or mitigate breast cancer progression. PDBP are natural, non-toxic, and affordable substances and have demonstrated excellent anti-breast cancer activities in inhibiting proliferation, migration, and invasion, and promoting apoptosis both in vitro and in vivo, thus effectively preventing or inhibiting breast cancer. However, there are no comprehensive reviews summarizing the effects and mechanisms of PDBP on the treatment of breast cancer. Therefore, this review described the inhibitory effects and mechanisms of active peptides from different plant protein sources on breast cancer. Additionally, we summarized the advantages and preparation methods of plant protein-derived anticancer peptide-encapsulated nanoparticles and their effects in inhibiting breast cancer. This review provides a scientific basis for understanding the anti-breast cancer mechanisms of PDBP and offers guidance for the development of therapeutic adjuvants enriched with these peptides.

Soft extracellular matrix drives endoplasmic reticulum stress-dependent S quiescence underlying molecular traits of pulmonary basal cells

Cell culture on soft matrix, either in 2D and 3D, preserves the characteristics of progenitors. However, the mechanism by which the mechanical microenvironment determines progenitor phenotype, and its relevance to human biology, remains poorly described. Here we designed multi-well hydrogel plates with a high degree of physico-chemical uniformity to reliably address the molecular mechanism underlying cell state modification driven by physiological stiffness. Cell cycle, differentiation and metabolic activity could be studied in parallel assays, showing that the soft environment promotes an atypical S-phase quiescence and prevents cell drift, while preserving the differentiation capacities of human bronchoepithelial cells. These softness-sensitive responses are associated with calcium leakage from the endoplasmic reticulum (ER) and defects in proteostasis and enhanced basal ER stress. The analysis of available single cell data of the human lung also showed that this non-conventional state coming from the soft extracellular environment is indeed consistent with molecular feature of pulmonary basal cells. Overall, this study demonstrates that mechanical mimicry in 2D culture supports allows to maintain progenitor cells in a state of high physiological relevance for characterizing the molecular events that govern progenitor biology in human tissues. STATEMENT OF SIGNIFICANCE: This study focuses on the molecular mechanism behind the progenitor state induced by a soft environment. Using innovative hydrogel supports mimicking normal human lung stiffness, the data presented demonstrate that lung mechanics prevent drift while preserving the differentiation capabilities of lung epithelial cells. Furthermore, we show that the cells are positioned in a quiescent state in the atypical S phase. Mechanistically, we demonstrate that this quiescence: i) is driven by calcium leakage from the endoplasmic reticulum (ER) and basal activation of the PERK branch of ER stress signalling, and ii) protects cells from lethal ER stress caused by metabolic stress. Finally, we validate using human single-cell data that these molecular features identified on the soft matrix are found in basal lung cells. Our results reveal original and relevant molecular mechanisms orchestrating cell fate in a soft environment and resistance to exogenous stresses, thus providing new fundamental and clinical insights into basal cell biology.

Naked mole-rats resist the accumulation of hypoxia-induced oxidative damage

Naked mole-rats are among the few mammals with the ability to endure severe hypoxia. These unique rodents use metabolic rate depression along with various molecular mechanisms to successfully overcome the challenges of oxygen-limitation, which they experience in their underground borrows. While studies have reported that naked mole-rats exhibit inherently higher levels of oxidative damage across their lifespan as compared to mice, it has yet to be determined whether naked mole-rats are vulnerable to oxidative damage during periods of low oxygen exposure. To investigate this phenomenon, we examined cellular oxidative damage markers of macromolecules: DNA oxidation determined as 8-oxo-2'deoxyguanosine (8-OHdG8) levels, RNA oxidation as 8-hydroxyguanosine (8-OHG), protein carbonylation, and lipid peroxidation in normoxic (control), acute (4 h at 7% O₂), and chronic (24 h at 7% O₂) hypoxia-exposed naked mole-rats. Brain appears to be the most resilient organ to hypoxia-induced oxidative damage, with both brain and heart exhibiting enhanced antioxidant capacity during hypoxia. Levels of DNA and RNA oxidation were minimally changed in all tissues and no changes were observed in protein carbonylation. Most tissues experienced lipid peroxidation, with liver displaying a 9.6-fold increase during hypoxia. Concomitantly, levels of DNA damage repair proteins were dynamically regulated in a tissue-specific manner, with white adipose displaying a significant reduction during hypoxia. Our findings show that naked mole-rats largely avoid hypoxia-induced oxidative damage, possibly due to their high tolerance to redox stress, or to reduced oxidative requirements made possible during their hypometabolic response when oxygen supply is limited.

Hedyotis diffusae Herba-Andrographis Herba inhibits the cellular proliferation of nasopharyngeal carcinoma and triggers DNA damage through activation of p53 and p21

Dysregulation of the cell cycle and the resulting aberrant cellular proliferation has been highlighted as a hallmark of cancer. Certain traditional Chinese medicines can inhibit cancer growth by inducing cell cycle arrest. In this study we explore the effect of Hedyotis diffusae Herba-Andrographis Herba on the cell cycle of nasopharyngeal carcinoma (NPC). Hedyotis diffusae Herba-Andrographis Herba-containing serum was prepared and then added to the cell culture medium. BrdU, comet, and FUCCI assays, western blot analysis and flow cytometry analysis revealed that Hedyotis diffusae Herba-Andrographis Herba treatment significantly alters cell proliferation, DNA damage, and cell cycle distribution. Xenograft mouse model experiments were performed, confirming these in vitro findings in vivo. Treatment with Hedyotis diffusae Herba-Andrographis Herba inhibited cell proliferation, promoted DNA damage, and arrested NPC cells progression from G1 to S phase. Further examination of the underlying molecular mechanisms revealed that treatment with Hedyotis diffusae Herba-Andrographis Herba increased the expression of p53 and p21, while reducing that of CCND1, Phospho-Rb, E2F1, γH2AX, and Ki-67 both in vivo and in vitro. Conversely, the inhibition of p53 and p21 could abolish the promoting effect of Hedyotis diffusae Herba-Andrographis Herba on the NPC cell cycle arrest at the G1 phase, contributing to the proliferation of NPC cells. Hedyotis diffusae Herba-Andrographis Herba suppressed the tumor growth in vivo. Overall, these findings suggest that Hedyotis Diffusae Herba-Andrographis prevent the progression of NPC by inducing NPC cell cycle arrest at the G1 phase through a p53/p21-dependent mechanism, providing a novel potential therapeutic treatment against NPC.

A developmentally programmed splicing failure contributes to DNA damage response attenuation during mammalian zygotic genome activation

Transition from maternal to embryonic transcriptional control is crucial for embryogenesis. However, alternative splicing regulation during this process remains understudied. Using transcriptomic data from human, mouse, and cow preimplantation development, we show that the stage of zygotic genome activation (ZGA) exhibits the highest levels of exon skipping diversity reported for any cell or tissue type. Much of this exon skipping is temporary, leads to disruptive noncanonical isoforms, and occurs in genes enriched for DNA damage response in the three species. Two core spliceosomal components, Snrpb and Snrpd2, regulate these patterns. These genes have low maternal expression at ZGA and increase sharply thereafter. Microinjection of Snrpb/d2 messenger RNA into mouse zygotes reduces the levels of exon skipping at ZGA and leads to increased p53-mediated DNA damage response. We propose that mammalian embryos undergo an evolutionarily conserved, developmentally programmed splicing failure at ZGA that contributes to the attenuation of cellular responses to DNA damage.

Restoring p53 Function in Head and Neck Squamous Cell Carcinoma to Improve Treatments

TP53 mutation is one of the most frequent genetic alterations in head and neck squamous cell carcinoma (HNSCC) and results in an accumulation of p53 protein in tumor cells. This makes p53 an attractive target to improve HNSCC therapy by restoring the tumor suppressor activity of this protein. Therapeutic strategies targeting p53 in HNSCC can be divided into three categories related to three subtypes encompassing WT p53, mutated p53 and HPV-positive HNSCC. First, compounds targeting degradation or direct inhibition of WT p53, such as PM2, RITA, nutlin-3 and CH1iB, achieve p53 reactivation by affecting p53 inhibitors such as MDM2 and MDMX/4 or by preventing the breakdown of p53 by inhibiting the proteasomal complex. Second, compounds that directly affect mutated p53 by binding it and restoring the WT conformation and transcriptional activity (PRIMA-1, APR-246, COTI-2, CP-31398). Third, treatments that specifically affect HPV+ cancer cells by targeting the viral enzymes E6/E7 which are responsible for the breakdown of p53 such as Ad-E6/E7-As and bortezomib. In this review, we describe and discuss p53 regulation and its targeting in combination with existing therapies for HNSCC through a new classification of such cancers based on p53 mutation status and HPV infection.

CXCL2-mediated ATR/CHK1 signaling pathway and platinum resistance in epithelial ovarian cancer

Tumor microenvironment and chemokines play a significant role in cancer chemoresistance. This study was designed to reveal the important role of CXCL2 in platinum resistance in epithelial ovarian cancer (EOC). Differently expressed (DE) genes were screen out based on analysis of GSE114206 dataset in GEO database. The expression of DE chemokines was further validated in platinum- resistant and sensitive EOC. Cell viability assay and cell apoptosis assay were performed to explore the roles of CXCL2 in EOC. Cell stemness characteristics and the signaling pathway regulated by CXCL2 were also investigated in this study. As the results showed, CXCL2 was identified up-regulated in platinum-resistant EOC. The functional assays showed overexpressing CXCL2 or co-culturing with recombinant human CXCL2 promoted cell resistance to cisplatin. Conversely, knocking down CXCL2 or co-culturing with neutralizing antibody to CXCL2 increased cell response to cisplatin. CXCL2 overexpressing maintained cell stemness and activated ATR/CHK1 signaling pathway in EOC. Moreover, we further demonstrated that CXCL2-mediated resistance to cisplatin could be saved by SB225002, the inhibitor of CXCL2 receptor, as well as be rescued by SAR-020106, the inhibitor of ATR/CHK1 signaling pathway. This study identified a CXCL2-mediated mechanism in EOC platinum resistance. Our findings provided a novel target for chemoresistance prevention in EOC.

Time-dependent genomic response in primary human uroepithelial cells exposed to arsenite for up to 60 days

Evidence from both in vivo and in vitro studies suggests that gene expression changes from long-term exposure to arsenite evolve markedly over time, including reversals in the direction of expression change in key regulatory genes. In this study, human uroepithelial cells from the ureter segments of 4 kidney-donors were continuously treated in culture with arsenite at concentrations of 0.1 or 1 μM for 60 days. Gene expression at 10, 20, 30, 40, and 60 days was determined using Affymetrix human genome microarrays and signal pathway analysis was performed using GeneGo Metacore. Arsenic treated cells continued to proliferate for the full 60-day period, whereas untreated cells ceased proliferating after approximately 30 days. A peak in the number of gene changes in the treated cells compared to untreated controls was observed between 30 and 40 days of exposure, with substantially fewer changes at 10 and 60 days, suggesting remodeling of the cells over time. Consistent with this possibility, the direction of expression change for a number of key genes was reversed between 20 and 30 days, including CFOS and MDM2. While the progression of gene changes was different for each subject, a common pattern was observed in arsenic treated cells over time, with early upregulation of oxidative stress responses (HMOX1, NQ01, TXN, TXNRD1) and down-regulation of immune/inflammatory responses (IKKα). At around 30 days, there was a transition to increased inflammatory and proliferative signaling (AKT, CFOS), evidence of epithelial-to-mesenchymal transition (EMT), and alterations in DNA damage responses (MDM2, ATM). A common element in the changing response of cells to arsenite over time appears to involve up-regulation of MDM2 by inflammatory signaling (through AP-1 and NF-κB), leading to inhibition of P53 function.

Influence of Kv11.1 (hERG1) K+ channel expression on DNA damage induced by the genotoxic agent methyl methanesulfonate

Besides their crucial role in cell electrogenesis and maintenance of basal membrane potential, the voltage-dependent K⁺ channel Kv11.1/hERG1 shows an essential impact in cell proliferation and other processes linked to the maintenance of tumour phenotype. To check the possible influence of channel expression on DNA damage responses, HEK293 cells, treated with the genotoxic agent methyl methanesulfonate (MMS), were compared with those of a HEK-derived cell line (H36), permanently transfected with the Kv11.1-encoding gene, and with a third cell line (T2) obtained under identical conditions as H36, by permanent transfection of another unrelated plasma membrane protein encoding gene. In addition, to gain some insights about the canonical/conduction-dependent channel mechanisms that might be involved, the specific erg channel inhibitor E4031 was used as a tool. Our results indicate that the expression of Kv11.1 does not influence MMS-induced changes in cell cycle progression, because no differences were found between H36 and T2 cells. However, the canonical ion conduction function of the channel appeared to be associated with decreased cell viability at low/medium MMS concentrations. Moreover, direct DNA damage measurements, using the comet assay, demonstrated for the first time that Kv11.1 conduction activity was able to modify MMS-induced DNA damage, decreasing it particularly at high MMS concentration, in a way related to PARP1 gene expression. Finally, our data suggest that the canonical Kv11.1 effects may be relevant for tumour cell responses to anti-tumour therapies.

Novel modulators of p53-signaling encoded by unknown genes of emerging viruses

The p53 transcription factor plays a key role both in cancer and in the cell-intrinsic response to infections. The ORFEOME project hypothesized that novel p53-virus interactions reside in hitherto uncharacterized, unknown, or hypothetical open reading frames (orfs) of human viruses. Hence, 172 orfs of unknown function from the emerging viruses SARS-Coronavirus, MERS-Coronavirus, influenza, Ebola, Zika (ZIKV), Chikungunya and Kaposi Sarcoma-associated herpesvirus (KSHV) were de novo synthesized, validated and tested in a functional screen of p53 signaling. This screen revealed novel mechanisms of p53 virus interactions and two viral proteins KSHV orf10 and ZIKV NS2A binding to p53. Originally identified as the target of small DNA tumor viruses, these experiments reinforce the notion that all viruses, including RNA viruses, interfere with p53 functions. These results validate this resource for analogous systems biology approaches to identify functional properties of uncharacterized viral proteins, long non-coding RNAs and micro RNAs.

New viruses are constantly emerging. The ORFEOME project was based on the hypothesis that every virus, regardless of its molecular makeup and biology should encode functions that intersect the p53 signaling network, since p53 guards the cell from genomic insults, of which depositing a foreign, viral nucleic acid is one. The result of the ORFEOME screen of proteins without any known function, of predicted open reading frames and of suspected non-coding RNAs is the identification of two viral proteins that interact with p53. The first one, orf10, is encoded by Kaposi Sarcoma-associated herpesvirus and the second one, NS2A, is encoded by the Zika virus.

An Unusual Case of Metastatic Basal Cell Carcinoma of the Prostate: A Case Report and Literature Review

Background: Primary basal cell carcinoma (BCC) is a rare prostate cancer. Currently, a standard treatment regime for BCC of the prostate is lacking and most patients have a poor prognosis. We reported on a patient with BCC of the prostate whose cancer metastasized after undergoing a radical prostatectomy and whose prognosis improved after treatment with etoposide.

Case Presentation: A 62-year-old male with a history of seminoma was admitted complaining of intermittent gross hematuria for 1 month. Following a prostate biopsy, the patient was diagnosed with BCC of the prostate and received radical prostatectomy and radiotherapy. Initially, the patient's symptoms improved; however, 2 years later, a chest computed tomography (CT) scan revealed lung nodules. The patient did not exhibit any symptoms of BCC of the prostate; however, pathological examination and immunohistochemical staining of the nodules confirmed metastatic BCC of the prostate. Chemotherapy with docetaxel and cisplatin was well-tolerated but did not slow disease progression. Next-generation sequencing revealed mutations in the ataxia telangiectasia-mutated (ATM), SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily b-member 1 (SMARCB1), and phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1) genes. The patient did not receive targeted therapy owing to financial limitations and instead, etoposide was administered. A 9-month follow-up chest CT scan showed an 80% reduction in existing lung nodules and no new nodules had developed.

Conclusion: Our patient, diagnosed with recurrent prostate BCC after receiving a radical prostatectomy, responded to treatment with etoposide. Radical prostatectomy and radiotherapy should remain first-line therapy; however, etoposide may be an alternative second-line therapy when other options are not available. Consensus regarding treatment plans, and the molecular mechanisms behind prostate BBC, must be elucidated.

Signal Pathways and Therapeutic Prospects of Diffuse Large B Cell Lymphoma

BACKGROUND

Diffuse Large B Cell Lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma which is heterogeneous both clinically and morphologically. Over the past decades, significant advances have been made in the understanding of the molecular genesis, leading to the identification of multiple pathways and molecules that can be targeted for clinical benefit.

OBJECTIVE

The current review aims to present a brief overview of signal pathways of DLBCL, which mainly focus on B-cell antigen Receptor (BCR), Nuclear Factor-κB (NF-κB), Phosphatidylinositol-3-Kinase (PI3K) - protein kinase B (Akt) - mammalian Target of Rapamycin (mTOR), Janus Kinase (JAK) - Signal Transducer and Activator (STAT), Wnt/β-catenin, and P53 pathways.

METHODS

Activation of signal pathways may contribute to the generation, development, chemotherapy sensitivity of DLBCL, and expression of pathway molecules is associated with the prognosis of DLBCL. Some agents targeting these pathways have been proved effective and relevant clinical trials are in progress. These agents used single or combined with chemotherapy/each other might raise the possibility of improving clinical outcomes in DLBCL.

CONCLUSION

This review presents several signal pathways of DLBCL and targeted agents had a tendency to improve the curative effect, especially in high-risk or relapsed/refractory DLBCL.

Prognostic Significance of Murine Double Minute 2 Expression in Tumor Cells in Upper Tract Urothelial Carcinoma: An Analysis of 341 Cases in a Large Chinese Center

Aims: The prognostic significance of murine double minute 2 (MDM2) expression remains unknown in patients with upper tract urothelial carcinoma (UTUC). This study was designed to evaluate MDM2 expression and its association with clinicopathological characteristics and tumor outcomes in UTUC patients. Materials and Methods: Expression levels of MDM2 and p53 were determined by immunohistochemistry in a cohort of 341 UTUC patients. Associations of MDM2 and p53 expression levels with clinicopathological characteristics, disease-free survival (DFS), cancer-specific survival (CSS), and intravesical recurrence-free survival (IVRFS) were analyzed. Results: Nuclear expression of MDM2 and p53 were detected in the tumor cells of 129 (37.8%) and 203 (59.5%) patients, respectively. Decreased p53 expression was associated with positive MDM2 staining in tumor cells (p = 0.002). MDM2 expression was correlated with the exposure to aristolochic acids (p = 0.020), better preoperative renal function (p = 0.016), ureter location (p = 0.002), higher pathological T stage (p = 0.006), high tumor grade (p < 0.001), presence of glandular differentiation (p = 0.036), and sarcoma differentiation (p = 0.020). Kaplan-Meier analysis showed that positive MDM2 staining was associated with shorter CSS (p < 0.001), DFS (p < 0.001), and IVRFS (p = 0.020); MDM2+/p53- was associated with shorter CSS (p < 0.001) and DFS (p < 0.001), but not IVRFS (p = 0.145); while CSS, DFS, and IVRFS did not differ significantly between the p53+ and p53- patients (p = 0.307, 0.089, and 0.198, respectively). Multivariate analyses revealed that MDM2 expression in tumor cells independently predicted shorter CSS (p < 0.001; hazard ratio [HR] = 2.600; 95% confidence interval [CI]: 1.625-4.161) and DFS (p < 0.001; HR = 1.863; 95% CI: 1.314-2.641), excepting IVRFS (p = 0.092; HR = 1.590; 95% CI: 0.928-2.726). Conclusions: UTUC patients with elevated MDM2 expression may exhibit more aggressive biological features of the tumor and tend to have shorter CSS and DFS.

Hsa_circ_0001546 acts as a miRNA-421 sponge to inhibit the chemoresistance of gastric cancer cells via ATM/Chk2/p53-dependent pathway

Circular RNAs (circRNAs) are a new class of noncoding RNAs, play a crucial role in tumor initiation and development. Hsa_circ_0001546 is a novel circular RNA that was downregulated in gastric cancer (GC) tissues, however its function and mechanism in GC has not been studied. Our study verified that circ_0001546 was decreased in GC and correlated with the poor prognosis. Next, Pull-down assay and dual-luciferase reporter assay verified that miR-421 was a target of circ_0001546 while ATM (Ataxia telangiectasia mutated) was target by miR-421. Overexpression of circ_0001546 inhibited the proliferation and chemoresistance of HGC-27 cells, and increased the expression of ATM. In addition, circ_0001546 overexpression reversed the effect of miR-421 overexpression. What is more, circ_0001546 inhibits the chemoresistance of HGC-27 cells to L-OPH (Oxaliplatin) may through the activation of the ATM/checkpoint kinase 2 (Chk2)/p53-dependent signaling pathway. In summary, our study proved that circ_0001546 sponges miR-421 to upregulate the expression level of ATM and inhibit the proliferation and chemoresistance through the activation of the ATM/Chk2/p53-dependent pathway.

P53/PUMA are potential targets that mediate the protection of brain-derived neurotrophic factor (BDNF)/TrkB from etoposide-induced cell death in neuroblastoma (NB)

The over-expressions of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor TrkB have been reported to induce chemo-resistance in neuroblastoma (NB) cells. In this study, we investigated the roles of P53 and BCL2 family members in the protection of BDNF/TrkB from etoposide-induced NB cell death. TB3 and TB8, two tetracycline (TET)-regulated TrkB-expressing NB cell lines, were utilized. The expressions of P53 and BCL2 family members were detected by Western blot or RT-PCR. Transfection of siRNAs was used to knockdown P53 or PUMA. Activated lentiviral was used to over-express PUMA. Cell survival was performed by MTS assay, and the percentage of cell confluence was measured by IncuCyte ZOOM. Our results showed that etoposide treatment induced significant and time-dependent increase of P53, which could be blocked by pre-treatment with BDNF, and knockdown P53 by transfecting siRNA attenuated etoposide-induced TrkB-expressing NB cell death. PUMA was the most significantly changed BCL2 family member after treatment with etoposide, and pre-treatment with BDNF blocked the increased expression of PUMA. Transfection with siRNA inhibited etoposide-induced increased expression of PUMA, and attenuated etoposide-induced NB cell death. We also found that over-expression of PUMA by infection of activated lentiviral induced TrkB-expressing NB cell death in the absence of etoposide, and treatment of BDNF protected NB cells from PUMA-induced cell death. Our results suggested that P53 and PUMA may be potential targets that mediated the protection of BDNF/TrkB from etoposide-induced NB cell death.

Growth arrest-specific gene 2 suppresses hepatocarcinogenesis by intervention of cell cycle and p53-dependent apoptosis

BACKGROUND

Growth arrest-specific gene 2 (GAS2) plays a role in modulating in reversible growth arrest cell cycle, apoptosis, and cell survival. GAS2 protein is universally expressed in most normal tissues, particularly in the liver, but is depleted in some tumor tissues. However, the functional mechanisms of GAS2 in hepatocellular carcinoma (HCC) are not fully defined.

AIM

To investigate the function and mechanism of GAS2 in HCC.

METHODS

GAS2 expression in clinic liver and HCC specimens was analyzed by real-time PCR and western blotting. Cell proliferation was analyzed by counting, MTS, and colony formation assays. Cell cycle analysis was performed by flow cytometry. Cell apoptosis was investigated by Annexin V apoptosis assay and western blotting.

RESULTS

GAS2 protein expression was lower in HCC than in normal tissues. Overexpression of GAS2 inhibited the proliferation of HCC cells with wide-type p53, while knockdown of GAS2 promoted the proliferation of hepatocytes (P < 0.05). Furthermore, GAS2 overexpression impeded the G1-to-S cell cycle transition and arrested more G1 cells, particularly the elevation of sub G1 (P < 0.01). Apoptosis induced by GAS2 was dependent on p53, which was increased by etoposide addition. The expression of p53 and apoptosis markers was further enhanced when GAS2 was upregulated, but became diminished upon downregulation of GAS2. In the clinic specimen, GAS2 was downregulated in more than 60% of HCCs. The average fold changes of GAS2 expression in tumor tissues were significantly lower than those in paired non-tumor tissues (P < 0.05).

CONCLUSION

GAS2 plays a vital role in HCC cell proliferation and apoptosis, possibly by regulating the cell cycle and p53-dependent apoptosis pathway.

Liver kinase B1/adenosine monophosphate-activated protein kinase signaling axis induces p21/WAF1 expression in a p53-dependent manner

Liver kinase B1 (LKB1) encodes a serine/threonine kinase and functions as a tumor suppressor. LKB1 loss-of-function somatic mutations are frequently observed in sporadic types of cancer, particularly in lung cancer. Ectopic LKB1 induces growth arrest by upregulating p21/cyclin dependent kinase inhibitor 1A (WAF1) in LKB1 deficient cervical and melanoma cancer cell lines. However, the underlying molecular mechanism remains to be elucidated. The present study built upon previous observations by confirming that the ectopic expression level of LKB1 significantly reduced colony formation of LKB1-deficient lung cancer cells. Mechanistically, the present study demonstrated that LKB1 overexpression significantly induced p21/WAF1 expression in a kinase-dependent manner. Conversely, LKB1 stable knockdown resulted in a decrease in p21/WAF1 expression level in colon cancer cells. In addition, it was revealed that pharmacological activation of adenosine monophosphate protein kinase (AMPK) by 2-deoxyglucose significantly increased the p21/WAF1 expression level, suggesting that AMPK acts downstream of LKB1 to induce p21/WAF1 expression. Furthermore, the present study demonstrated that functional p53 was required for p21/WAF1 induction by LKB1. Phosphorylation of p53-Ser¹⁵ was increased by ectopic LKB1 or AMPK activation. Taken together, these results suggested that LKB1 acts via its substrate, AMPK, to upregulate p21/WAF1 expression in a p53-dependent manner. Therefore, the present study identified an important signaling axis, providing novel molecular insights into the tumor suppressor role of LKB1.

Low dose arsenite confers resistance to UV induced apoptosis via p53-MDM2 pathway in ketatinocytes

Chronic arsenite and ultraviolet (UV) exposure are associated with skin tumor. To investigate the details by low concentrations of arsenite and UV induced carcinogenesis in skin, hTERT-immortalized human keratinocytes were used as a cellular model with exposure to low concentrations of sodium arsenite and UV. The effect of NaAsO₂ on UV treatment-induced apoptosis was measured by flow cytometry and Hoechst staining. We found that the cell apoptosis induced by UV exposure was significantly attenuated after exposure to low-dose arsenite, and knockdown of p53 could block UV-induced apoptosis indicating that this phenomenon depended on p53. Interestingly, the expression of murine double minute 2 (MDM2), including its protein and transcriptional levels, was remarkably high after exposure to low-dose arsenite. Moreover, low-dose arsenite treatment dramatically decreased the MDM2 gene promoter activity, suggesting that this effect has been mediated through transcription. In addition, treatment of PD98059 reversed low-dose arsenite-induced MDM2 expression, and the inhibition of ERK2 expression could significantly block MDM2 expression as a consequence, and p53 expression automatically was increased. To validate the role of p53 in exposure to low-dose arsenite, the expression of p53 was examined by immunohistochemistry in the skin of Sprague−Dawley rats model by chronic arsenite exposure for 6 months and in patients with arsenic keratosis, and the results showed that the expression of p53 was decreased in those samples. Taken together, our results demonstrated that low-dose arsenite-induced resistance to apoptosis through p53 mediated by MDM2 in keratinocytes.